Researchers have identified an enzyme that helps ensure egg and sperm cells contain the right number of chromosomes.

The finding may improve the understanding of meiosis and what happens when it goes wrong, leading to chromosome abnormalities such as Down's syndrome as well as miscarriages.

Meiosis is a specialised form of cell division that takes place in sperm and egg cells. It involves two rounds of cell division to ensure that each daughter cell ends up with half the original number of chromosomes. This means that after sex cells fuse, and the resulting embryo has two copies of each chromosome – one from each parent.

Errors in chromosome segregation can result in aneuploidy, in which daughter cells end up with too many or too few chromosomes. Aneuploidy causes conditions such as Down's syndrome, in which there are three copies of chromosome 21, and it is a leading cause of miscarriage.

'Understanding how meiosis is regulated is of great importance to understanding the causes of aneuploidy and genetic disorders,' said Dr Gary Kerr of the University of Salford and co-author of the paper.

Dr Prakash Arumugam of the National University of Singapore led the team, which examined the role of the enzyme PP2ACdc55 in meiosis by looking at how it works in budding yeast. Meiosis in yeast is remarkably similar to meiosis in mammals, but is much easier to study. The researchers created a series of random mutations in the Cdc55 gene to create 987 mutant strains of yeast, adding fluorescent tags so they could track what happens to their chromosomes during meiosis.

Previous research had shown that PP2ACdc55 plays a key role in the timing of meiosis, preventing cells dividing before their chromosomes have been segregated equally into two daughter cells. This study, which was published in Scientific Reports, found that PP2ACdc55 also plays a role in separating chromosome pairs into the two daughter cells.

The researchers now plan to study the role of this crucial enzyme in mammals.

Although our recent findings on the fate of aneuploid cells in mosaic embryos have indeed been somewhat misrepresented in the press, our findings may still constitute a strand of hope for mothers who have had early test results showing mosaic aneuploidy...

Press coverage of a recent study on mouse embryos speculates that termination of human pregnancies diagnosed with aneuploidy (a family of conditions including Down's syndrome) at prenatal diagnosis could be unnecessary, due to the ability of the fetus to 'heal itself'. In fact, the paper's findings are not relevant to aneuploidy detected at prenatal diagnosis...